How do you pass the battle where you have to rescue Derihourai (the guy wielding 2 t-baton like things)? Everytime he dies before i can get to him. Not helping is the ground where Haku's party is is easily blocked by a single person and i have no ranged attacks (magic requires the girls not to move=too slow). How do you guys get pass this level? Restarting the level over and over won't help as Deri and Co won't level up and it's them that's doing the dying.

Probably depends largely on difficulty, but what worked for me (hard 1 or something) was pulling the whole Derihourai group as far back as possible and using his troops as meatshield to surround him (don't even move them 1 square closer to surround enemies, that can be enough to make more enemies flock that way), while disregarding formation with Hakuoro's group to advance as fast as possible, if you do it right most enemies will head towards your upper characters instead of Derihoura's troops - even more when you get more troops past the bottleneck.

The only time I can complete this in hard mode is when the AI fails completely or by abusing the AI.

What I did was I made sure derihourai was all the way in the back, west most corner or top side of the corner. I put all of his troops next to him. When there is no path or no way to attack derihourai, the AI or the enemies will go for hakuruo if there is a path leading to him. So 2 archers and maybe 1-2 swordsman will leave derihourai and go for hakurou.